1. Field of the Invention
The present invention relates to a disc brake assembly for wheeled vehicles, and more particularly to a disc brake assembly which includes a pair of brake pads disposed at opposite sides of a disc rotor. The pads are movably mounted on a stationary mounting for movement toward and away from the rotor to frictionally brake the rotor.
2. Description of the Prior Art
A conventional disc brake assembly of this kind is disclosed, for example, in Japanese Patent Publication No. 45-36695 published on Nov. 21, 1970. This conventional disc brake assembly includes a pair of pads on backing plates whose circumferential end surfaces (i.e., the surfaces located at the ends spaced in the rotational direction of the disc rotor) are inclined to diverge in a radially outward direction. The mounting member has correspondly shaped torsion-resisting surfaces and a spring member urging the brake pad toward the axial center of the disc rotor. In this disc brake assembly, the friction forces act against the brake pad in a tangential direction with reference to the axis of rotation of the disc rotor at the nearly center portion (press center) of the brake pad when the disc brake assembly is operated. This friction force is resolved into a generally radial outward component force and a component force generally perpendicular thereto. The brake pads are forced to slide along the torque receiving mounting surface radially outwardly against the bias of the spring member by the radially outward friction force component. The disc brake assembly attempts to prevent vibration of the brake pad by offsetting that radially outward friction force component by the force of the spring member.
Further, a conventional disc brake assembly is disclosed, for example, in Japanese Patent Laid-Open Publication No. 55-100432 published on Jul. 31, 1980. This conventional disc brake assembly includes a pair of brake pads whose backing plates have circumferential ends extending perpendicular to a tangent intersecting the pad at a nearly center portion (press center) of each brake pad. The mounting member has torque resisting surfaces located opposite and parallel to the circumferential ends of the backing plate. In this disc brake assembly, the friction force acts against the brake pad in a direction perpendicular to the torque resisting surface when the disc brake assembly is operated, whereby the brake pad is not urged radially outwardly by friction forces.
In the first-discussed conventional disc brake assembly, the brake pads are outwardly slid along the torque resisting surface against the force of the spring member, but if the brake force (i.e., the depression force of the brake pedal) changes during the brake operation, the radially outward friction force component changes and the brake pad becomes unstable in the radial direction of the disc rotor. As a result, the brake pad is vibrated by the force of the spring member in the radial direction of the disc rotor.
Furthermore, in both of the afore-described disc brake assemblies, since the location of the press center of the brake pad is not regulated, the press center of the brake pad can be relocated diametrically and circumferentially depending upon the configuration of the apparatus, e.g., by the amount of concavity or convexity of the frictional surface of the brake pad, the arc of the disc rotor, a non-constant thickness of the disc rotor, a bending of the caliper member (i.e., the bridge portion of the caliper member bends so as to separate the reaction portion from the cylinder portion) and the inclination of the caliper member in the brake operation as shown in FIG. 23. As a result, the friction force acting tangentially against the brake pad at the press center is not applied perpendicularly to the torque resisting surface of the mounting member whereupon the brake pad is displaced radially.
The inventors of the present invention analyzed the relationship between the movement of the brake pads and the annoying squealing noise of the disc brake by various experiments. As a result, these inventors learned that since the prior art brake pads are instable and the press center of the brake pads can be located at various diametrical and circumferential locations when the disc brake assembly is operated, the brake pads 2 can be moved relative to the torque resisting surface 1a of the mounting member 1 as shown by an imaginary line in the FIG. 23. Further, annoying noises of the disc brake are generated when the brake pads are moving in that manner, but when the brake pads almost do not move, virtually no annoying noise is generated.
Further, in Japanese Patent Publication No. 58-18533 published on Apr. 13, 1983, a disc brake assembly is disclosed having a spring member which is fixed to the circumferential end of the backing plate of the brake pad in order to eliminate any gap between the torque resisting surface of the mounting member and the end surface of the backing plate. That arrangement prevents the brake pads from vibrating in the nonoperational condition of the disc brake assembly, and prevents the backing plate from bumping into the torque receiving surface in the first stage of the brake operation However, since the spring member is installed on the backing plate, it is necessary to remove the spring member (or exchange it along with the brake pad) when the brake pad is exchanged. Therefore, the effort involved in replacing the brake pad is increased and/or the cost of the disc brake assembly increases.